Method for sorting integrated circuit devices

ABSTRACT

An inventive method for sorting integrated circuit (IC) devices of the type having a substantially unique identification (ID) code, such as a fuse ID, includes automatically reading the ID code of each of the IC devices, and sorting the IC devices in accordance with their automatically read ID codes. The inventive method can be used in conjunction with an IC manufacturing process that includes providing semiconductor wafers, fabricating the IC&#39;s on each of the wafers, causing each of the IC&#39;s to store its ID code, separating each of the IC&#39;s from its wafer to form IC dice, assembling the IC dice into IC devices, and testing the IC devices. The inventive method is useful for, among other things, culling IC reject bins for shippable IC&#39;s, sorting IC&#39;s from a wafer lot into those that require enhanced reliability testing and those that do not, and allowing IC&#39;s fabricated using both a control fabrication process recipe and a new fabrication process recipe under test to be assembled and tested using the same equipment to reduce unintended test variables introduced when the IC&#39;s are assembled and tested separately.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to: a co-pending application havingSer. No. 08/785,353 entitled "METHOD FOR SORTING INTEGRATED CIRCUITDEVICES," and filed Jan. 17, 1997; a co-pending application having Ser.No. 08/591,238, entitled "METHOD AND APARATUS [sic] FOR STORAGE OF TESTRESULTS WITHIN AN INTEGRATED CIRCUIT," and filed Jan. 17, 1996; aco-pending application having Ser. No. 08/664,109, entitled "A STRUCTUREAND A METHOD FOR STORING INFORMATION IN A SEMICONDUCTOR DEVICE," andfiled Jun. 13, 1996; a divisional application having Serial No.(unknown), entitled "METHOD FOR SORTING INTEGRATED CIRCUIT DEVICES" andfiled concurrently herewith, a co-pending application having Ser. No.08/822,731, entitled "METHOD FOR CONTINUOUS, NON LOT-BASED INTEGRATEDCIRCUIT MANUFACTURING," and filed Mar. 24, 1997; a co-pendingapplication having Ser. No. 08/806,442, entitled "METHOD IN ANINTEGRATED CIRCUIT (IC) MANUFACTURING PROCESS FOR IDENTIFYING ANDRE-DIRECTING IC'S MIS-PROCESSED DURING THEIR MANUFACTURE," and filedFeb. 26, 1997; a co-pending application having Ser. No. 08/871,015,entitled "METHOD FOR USING DATA REGARDING MANUFACTURING PROCEDURESINTEGRATED CIRCUITS (IC'S) HAVE UNDERGONE, SUCH AS REPAIRS, TO SELECTPROCEDURES THE IC'S WILL UNDERGO, SUCH AS ADDITIONAL REPAIRS," and filedJun. 6, 1997; and a co-pending application having Ser. No. 08/801,565entitled "METHOD OF SORTING A GROUP OF INTEGRATED CIRCUIT DEVICES FORTHOSE DEVICES REQUIRING SPECIAL TESTING," and filed Feb. 17, 1997.

BACKGROUND

1. Field of the Invention

The present invention relates in general to integrated circuit (IC)manufacturing and, more specifically, to methods in IC manufacturingprocesses for sorting IC devices using identification (ID) codes, suchas fuse ID's, in the devices.

2. State of the Art

Integrated circuits (IC's) are small electronic circuits formed on thesurface of a wafer of semiconductor material, such as silicon, in an ICmanufacturing process referred to as "fabrication." Once fabricated,IC's are electronically probed to evaluate a variety of their electroniccharacteristics, cut from the wafer on which they were formed intodiscrete IC dice or "chips," and then assembled for customer use usingvarious well-known IC packaging techniques, including lead framepackaging, Chip-On-Board (COB) packaging, and flip-chip packaging.

Before being shipped to customers, packaged IC's are generally tested toensure they will function properly once shipped. Testing typicallyinvolves a variety of known test steps, such as pre-grade, burn-in, andfinal, which test IC's for defects and functionality and grade IC's forspeed. As shown in FIG. 1, IC's that pass the described testing aregenerally shipped to customers, while IC's that fail the testing aretypically rejected.

The testing standards for a particular IC product are sometimes relaxedas the product "matures" such that IC's previously rejected under stricttesting standards may pass the relaxed testing standards. Consequently,reject bins containing previously rejected IC's are sometimes "culled"for IC's that are shippable under relaxed testing standards by testingthe rejected IC's again using the relaxed testing standards.Unfortunately, while this "culling" process does retrieve shippable IC'sfrom reject bins, it makes inefficient use of expensive and oftenlimited testing resources by diverting those resources away from testinguntested IC's in order to retest previously rejected IC's. Therefore,there is a need in the art for an improved method of "culling" orsorting such reject bins for shippable IC's.

Similarly, as shown in FIG. 2, all the IC's from the wafers in a waferlot typically undergo enhanced reliability testing that is moreextensive and strict than normal testing when any of the wafers in thelot are deemed to be unreliable because of fabrication or other processerrors. Since a wafer lot typically consists of fifty or more wafers,many of the IC's that undergo the enhanced reliability testing do notrequire it because they come from wafers that are not deemed unreliable.Performing enhanced reliability testing on IC's that do not need it isinefficient because such testing is typically more time-consuming anduses more resources than normal testing. Therefore, there is a need inthe art for a method of sorting IC's from a wafer lot into those IC'sthat require enhanced reliability testing and those that do not.

Likewise, as shown in FIG. 3, a new or special "recipe" for fabricatingIC's on wafers is sometimes tested by fabricating some wafers from awafer lot using the special recipe and other wafers from the wafer lotusing a control recipe. IC's from the wafers then typically undergoseparate assembly and test procedures so that the test results of IC'sfabricated using the special recipe are not mixed with the test resultsof IC's fabricated using the control recipe, and vice versa. Testreports from the separate test procedures are then used to evaluate thespecial recipe and to determine whether the IC's are to be shipped tocustomers, reworked, repaired, retested, or rejected. Unfortunately,because the IC's undergo separate test and assembly procedures,undesirable variables, such as differences in assembly and testequipment, are introduced into the testing of the special recipe. Itwould be desirable, instead, to be able to assemble and test the IC'susing the same assembly and test procedures, and to then sort the IC'sand their test results into those IC's fabricated using the specialrecipe and those IC's fabricated using the control recipe. Therefore,there is a need in the art for a method of identifying individual IC'sfabricated using a special or control recipe and sorting the IC's basedon their fabrication recipe.

As described above, IC's are typically tested for variouscharacteristics before being shipped to customers. For example, as shownin FIG. 4, IC's may be graded in test for speed and placed in variousbins (e.g., 5 nanoseconds (ns), 6 ns, and 7 ns bins) according to theirgrading. If a customer subsequently requests a more stringent speedgrade (e.g., 4 ns), IC's in one of the bins (e.g., a 5 ns bin) arere-tested and thereby sorted into IC's that meet the more stringentspeed grade (e.g., 4 ns bin) and those that do not (e.g., 5 ns bin).While this conventional process sorts the IC's into separate speedgrades, it makes inefficient use of expensive and often limited testingresources by diverting those resources away from testing untested IC'sin order to retest previously tested IC's. Therefore, there is a need inthe art for an improved method of "culling" or sorting bins for IC'sthat meet more stringent standards, such as a higher speed grading.

As described in U.S. Pat. Nos. 5,301,143, 5,294,812, and 5,103,166, somemethods have been devised to electronically identify individual IC's.Such methods take place "off" the manufacturing line, and involve theuse of electrically retrievable ID codes, such as so-called "fuse ID's,"programmed into individual IC's to identify the IC's. The programming ofa fuse ID typically involves selectively blowing an arrangement of fusesand anti-fuses in an IC so that when the fuses or anti-fuses areaccessed, they output a selected ID code. Unfortunately, none of thesemethods addresses the problem of identifying and sorting IC's "on" amanufacturing line.

SUMMARY OF THE INVENTION

An inventive method for sorting integrated circuit (IC) devices of thetype to have a substantially unique identification (ID) code, such as afuse ID, includes automatically reading the ID code of each of the ICdevices and sorting the IC devices according to their automatically readID codes. The inventive method can be used in conjunction with an ICmanufacturing process that includes providing semiconductor wafers,fabricating the IC's on each of the wafers, causing each of the IC's tostore its ID code, separating each of the IC's from its wafer to form anIC die, assembling the IC dice into IC devices, and testing the ICdevices. The method can also be used in conjunction with Single In-lineMemory Module (SIMM), Dual In-line Memory Module (DIMM), and othermulti-chip module (MCM) manufacturing processes.

In another embodiment, an inventive method for recovering IC devicesfrom a group of IC devices that have previously been rejected inaccordance with a test standard that has since been relaxed includes:storing test results that caused each of the IC devices in the group tobe rejected in connection with an ID code, such as a fuse ID, associatedwith each device; automatically reading the ID code from each of the ICdevices; accessing the test results stored in connection with each ofthe automatically read ID codes; comparing the accessed test results foreach of the IC devices with the relaxed test standard; and sorting theIC devices according to whether their accessed test results pass therelaxed test standard in order to recover any of the IC devices havingtest results that pass the relaxed test standard.

By sorting the IC devices in accordance with their previously storedtest results and their ID codes, the above-described inventive methodeliminates the need to retest the IC devices after the test standard isrelaxed in order to cull shippable IC devices from the rejected devices.

In still another embodiment, a method for sorting a group of IC devicesin accordance with a first IC standard, such as a speed standard, thathave previously been sorted in accordance with a second IC standard,such as a speed standard that is less stringent than the first, includesstoring test results that caused each of the IC devices in the group tobe sorted into the group in connection with ID codes, such as fuse ID's,of the devices, automatically reading the ID code from each of the ICdevices, accessing the test results stored in connection with each ofthe automatically read ID codes, comparing the accessed test results foreach of the IC devices with the first IC standard, and sorting the ICdevices according to whether their test results pass the first ICstandard.

In a further embodiment, an inventive back-end test method forseparating IC devices in need of enhanced reliability testing from agroup of IC devices undergoing back-end test procedures includes:storing a flag in connection with an ID code, such as a fuse ID,associated with each of the IC devices in the group indicating whethereach IC device is in need of enhanced reliability testing; automaticallyreading the ID code of each of the IC devices in the group; accessingthe enhanced reliability testing flag stored in connection with each ofthe automatically read ID codes; and sorting the IC devices inaccordance with whether their enhanced reliability testing flagindicates they are in need of enhanced reliability testing.

Thus, the inventive method described above provides an advantageousmethod for sorting IC's from the same wafer lot into those IC's thatrequire enhanced reliability testing and those that do not.

In a still further embodiment, an inventive method in an ICmanufacturing process for testing different fabrication process recipesincludes the following: providing first and second pluralities ofsemiconductor wafers; fabricating a first plurality of IC's on each ofthe first plurality of wafers in accordance with a control recipe;fabricating a second plurality of IC's on each of the second pluralityof wafers in accordance with a test recipe; causing each of the IC's oneach of the wafers to permanently store a substantially unique ID code,such as a fuse ID; separating each of the IC's on each of the wafersfrom its wafer to form one of a plurality of IC dice; assembling each ofthe IC dice into an IC device; automatically reading the ID code fromthe IC in each of the IC devices; testing each of the IC devices; andsorting each of the IC devices in accordance with the automatically readID code from the IC in each of the IC devices indicating the IC is fromone of the first and second pluralities of IC's.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram illustrating a conventional procedure in anintegrated circuit (IC) manufacturing process for culling shippable IC'sfrom a reject bin;

FIG. 2 is a flow diagram illustrating a conventional procedure in an ICmanufacturing process for directing IC's to enhanced reliabilitytesting;

FIG. 3 is a flow diagram illustrating a conventional procedure in an ICmanufacturing process for testing a new or special fabrication processrecipe;

FIG. 4 is a flow diagram illustrating a conventional procedure in an ICmanufacturing process for speed-sorting IC's;

FIG. 5 is a flow diagram illustrating a procedure in an integratedcircuit (IC) manufacturing process for culling shippable IC's from areject bin in accordance with the present invention;

FIG. 6 is a flow diagram illustrating a procedure in an IC manufacturingprocess for directing IC's to enhanced reliability testing in accordancewith another embodiment of the present invention;

FIG. 7 is a flow diagram illustrating a procedure in an IC manufacturingprocess for testing a new or special fabrication process recipe inaccordance with still another embodiment of the present invention; and

FIG. 8 is a flow diagram illustrating a procedure in an IC manufacturingprocess for speed-sorting IC's in accordance with a further embodimentof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 5, an inventive method for sorting integrated circuit(IC) devices is embodied in a method 10 in an IC manufacturing processfor culling shippable IC's from a reject bin 12. It will be understoodby those having skill in the field of this invention that the presentinvention is applicable to sorting any IC devices, including DynamicRandom Access Memory (DRAM) IC's, Static Random Access Memory (SRAM)IC's, Synchronous DRAM (SDRAM) IC's, processor IC's, Single In-lineMemory Modules (SIMM's), Dual In-line Memory Modules (DIMM's), and otherMulti-Chip Modules (MCM's).

The method 10 includes the step 14 of fabricating IC's on wafers from awafer lot 16. IC's fabricated on the wafers are then programmed in aprogram step 18 in the manner described above with a fuse identification(ID) unique to each IC. The fuse ID may identify a wafer lot ID, theweek the IC's were fabricated, a wafer ID, a die location on the wafer,and a fabrication facility ID. It will be understood, of course, thatthe present invention includes within its scope IC's having any ID code,including those having fuse ID's. It will also be understood that the IDcode for each IC need not be unique, but instead may only specify thewafer the IC comes from, for example.

Once programmed, the IC's proceed through an assembly step 20 to a teststep 22 where the fuse ID's are automatically read and stored inassociation with test data 24 generated in the test step 22. Althoughthe fuse ID's are typically read electronically, it will be understoodthat they may also be read optically if the fuse ID consists of "blown"laser fuses that are optically accessible. It will also be understoodthat the test data 24 may include data such as the following: dataidentifying the testing equipment that tested the IC's, operatingpersonnel who operated the testing equipment, and the set-up of theequipment when the IC's were tested; and data indicating the time anddate the IC's were tested, the yield of shippable IC's through the teststep 22, and test results for the IC's from the various stages of thetest step 22.

IC's that pass the test step 22 are typically shipped to customers,while those that fail the test step 22 are directed to the reject bin12. At a point in time when test standards of the test step 22 have beenrelaxed as described above, the IC's in the reject bin 12 are sorted ina sort step 26 by reading the fuse ID of each IC, accessing the testdata 24 associated with the fuse ID, and comparing the accessed testdata 24 with the relaxed test standards. Those IC's that fail even therelaxed test standards are directed back to the reject bin 12, whilethose IC's that pass the relaxed test standards are typically shipped tocustomers. The method 10 thus successfully culls shippable IC's from thereject bin 12 without retesting the IC's.

As shown in FIG. 6, the inventive sorting method is also embodied in abackend (i.e., after fabrication) test method 30 for separating IC's inneed of enhanced reliability testing from a group of IC's undergoingback-end test procedures. IC's typically require enhanced reliabilitytesting because the wafer they come from is unreliable as a result offabrication errors and other unintended manufacturing processdeviations.

The method 30 includes the step 32 of fabricating IC's on wafers from awafer lot 34. IC's fabricated on the wafers are then programmed in aprogram step 36 in the manner described above with a fuse identification(ID) unique to each IC. The fuse ID may identify a wafer lot ID, theweek the IC's were fabricated, a wafer ID, a die location on the wafer,and a fabrication facility ID. It will be understood, of course, thatthe present invention includes within its scope IC's having any ID code,including those having fuse ID's. It will also be understood that the IDcode for each IC need not be unique, but instead may only specify thewafer the IC comes from, for example.

Once programmed, the IC's proceed through an assembly step 38. At thispoint in the IC manufacturing process, it is not uncommon for a numberof wafers to have been identified as being unreliable for the reasonsstated above. The fuse ID's of the IC's that come from these unreliablewafers may then be associated with a stored flag indicating the IC'scome from unreliable wafers. If any wafers in the wafer lot 34 have beenidentified as being unreliable, the IC's proceed to a sort step 40,where their fuse ID's are automatically read so the IC's can be sortedinto those flagged as coming from the unreliable wafers that requireprocessing through an enhanced reliability testing step 42 and those notflagged as coming from the unreliable wafers that may proceed through astandard test step 44. Of course, those IC's that pass either thestandard test step 44 or the enhanced reliability testing step 42 aretypically shipped to customers, while those that fail these steps aredirected to a reject bin (not shown).

Thus, the present invention provides a method 30 that directs those IC'sneeding enhanced reliability testing to the enhanced reliability testingstep 42 while allowing those that do not require enhanced reliabilitytesting to proceed through the standard testing step 44.

As shown in FIG. 7, the inventive sorting method is further embodied ina method 50 for testing different fabrication process recipes. Suchtesting is typically done in accordance with a Special Work Request(SWR) from an engineer or technician.

The method 50 includes fabricating some of the wafers from a wafer lot52 in a fabrication step 54 in accordance with a control process recipethat is typically the normal process recipe in use in the ICmanufacturing process at the time. The remainder of the wafers from thewafer lot 52 are fabricated in another fabrication step 56 in accordancewith a special or test process recipe. The special or test processrecipe may change a variety of variables in the fabrication process,including doping, the thickness of IC layers, etc.

Once the IC's are fabricated in the fabrication steps 54 and 56, theIC's are then programmed in a program step 58 in the manner describedabove with a fuse identification (ID) unique to each IC. The fuse ID mayidentify a wafer lot ID, the week the IC's were fabricated, a wafer ID,a die location on the wafer, and a fabrication facility ID. It will beunderstood, of course, that the present invention includes within itsscope IC's having any ID code, including those having fuse ID's. It willalso be understood that the ID code for each IC need not be unique, butinstead may only specify the wafer the IC comes from, for example.

Once programmed, the IC's proceed through an assembly step 60 to a teststep 62 where the fuse ID's are automatically read and stored inassociation with test data 64 generated for both the control recipe IC'sand the special or test recipe IC's in the test step 62. Although thefuse ID's are typically read electronically, it will be understood thatthey may also be read optically if the fuse ID consists of "blown" laserfuses that are optically accessible. It will also be understood that thetest data 64 may include data such as the following: data identifyingthe testing equipment that tested the IC's, operating personnel whooperated the testing equipment, and the set-up of the equipment when theIC's were tested; and data indicating the time and date the IC's weretested, the yield of shippable IC's through the test step 62, and testresults for the IC's from the various stages of the test step 62.

Once the test data 64 is generated, the data 64 may be analyzed todetermine those IC's that are shippable and those that are not, and todetermine any differences in test results between the control recipeIC's and the special or test recipe IC's. The IC's are sorted in a sortstep 66 so they may be shipped, reworked, repaired, retested, orrejected in accordance with the analysis of the test results.

By sorting the control recipe and special or test recipe IC's at the endof the IC manufacturing process, the method 50 is able to assemble andtest the IC's together and thus eliminate unintended variablesintroduced into the process of testing the special or test recipe by theconventional method of assembling and testing the IC's separately. Theinventive method 50 thus provides more reliable test results.

As shown in FIG. 8, the inventive method for sorting IC devices is alsoembodied in a method 70 in an IC manufacturing process for sorting ICdevices in accordance with an IC standard, such as speed, that is morestringent than an IC standard that the devices were previously sorted inaccordance with. It will be understood that although the method of FIG.8 will be described with respect to speed-sorting, the method isapplicable to all situations in which IC's previously sorted inaccordance with an IC standard, such as speed, need to be sorted inaccordance with another, more stringent IC standard. Such IC standardsmay include, for example, access time, data setup time, data hold time,standby current, refresh current, and operating current.

The method 70 includes the step 72 of fabricating IC's on wafers from awafer lot 74. IC's fabricated on the wafers are then programmed in aprogram step 76 in the manner described above with a fuse identification(ID) unique to each IC. The fuse ID may identify a wafer lot ID, theweek the IC's were fabricated, a wafer ID, a die location on the wafer,and a fabrication facility ID. It will be understood, of course, thatthe present invention includes within its scope IC's having any ID code,including those having fuse ID's.

Once programmed, the IC's proceed through an assembly step 78 to a teststep 80 where the fuse ID's are automatically read and stored inassociation with test data 82 generated in the test step 80. Althoughthe fuse ID's are typically read electronically, it will be understoodthat they may also be read optically if the fuse ID consists of "blown"laser fuses that are optically accessible. It will also be understoodthat the test data 82 includes speed grading data for each IC, asdescribed above, and may include data such as the following: dataidentifying the testing equipment that tested the IC's, operatingpersonnel who operated the testing equipment, and the set-up of theequipment when the IC's were tested; and data indicating the time anddate the IC's were tested, the yield of shippable IC's through the teststep 80, and test results for the IC's from the various stages of thetest step 80.

IC's that pass the test step 80 are typically directed to speed gradedbins 84, 86, and 88, while those that fail the test step 80 are directedto a reject bin 90. The speed graded bins 84, 86, and 88 typically eachcontain IC's of varying speeds. For example, the bin 88 may contain avariety of 5.0 ns, 4.5 ns, 4.0 ns, 3.5 ns, etc. parts, the bin 86 maycontain a variety of 6.0 ns, 5.5 ns, 5.1 ns, etc. parts, and the bin 84may contain a variety of 7.0 ns, 6.5 ns, 6.1, etc. parts.

On occasion, customers request IC's that meet a more stringent speedstandard (e.g., 4 nanoseconds (ns)) than any of the IC's in the variousbins 84, 86, and 88 have been graded for. While bin 88, for example, maycontain IC's that will meet the more stringent speed standard, the bin88 cannot be used to supply the customer's request because the IC's inthe bin 88 have only been graded (i.e., are guaranteed to meet orexceed) a lower speed standard (e.g., 5 ns). Therefore, the presentinventive method 70 sorts the IC's in a sort step 92 by reading the fuseID of each IC, accessing the test data 82, including the speed-gradingdata, associated with the fuse ID, and comparing the accessedspeed-grading data with the more stringent speed standard (e.g., 4 ns).Those IC's that fail the more stringent speed standard are directed to aspeed graded bin 94, while those IC's that pass the more stringent speedstandard are directed to another speed graded bin 96 where they can beused to fill the customer's request. The inventive method 70 thus sortsthe IC's in accordance with a more stringent IC standard, such as speed,than they were previously sorted in accordance with without having toretest the IC's, and thus without reusing valuable testing resources toretest IC's.

Although the present invention has been described with reference toparticular embodiments, the invention is not limited to these describedembodiments. For example, while the various steps of the embodiments ofthe inventive sorting method have been described as occurring in aparticular order, it will be understood that these steps need notnecessarily occur in the described order to fall within the scope of thepresent invention. Thus, the invention is limited only by the appendedclaims, which include within their scope all equivalent methods thatoperate according to the principles of the invention as described.

What is claimed is:
 1. A back-end test method in an integrated circuit(IC) manufacturing process for separating IC devices in need of enhancedreliability testing from a group of IC devices undergoing back-end testprocedures, the IC devices being of the type having a substantiallyunique identification (ID) code, the method comprising:storing anenhanced reliability testing flag in connection with the ID code of eachof the IC devices in the group indicating whether each IC device is inneed of enhanced reliability testing; automatically reading the ID codeof each of the IC devices in the group; accessing the enhancedreliability testing flag stored in connection with each of theautomatically read ID codes; and sorting the IC devices in accordancewith whether their enhanced reliability testing flag indicates they arein need of enhanced reliability testing.
 2. A back-end test method in anintegrated circuit (IC) manufacturing process for separating IC devicesin need of enhanced reliability testing from a group of IC devicesundergoing back-end test procedures, the IC devices being of the typehaving a substantially unique identification (ID) code, the methodcomprising:storing an enhanced reliability testing flag in connectionwith the ID code of each of the IC devices in the group indicatingwhether each IC device is in need of enhanced reliability testing;automatically reading the ID code of each of the IC devices in thegroup; accessing the enhanced reliability testing flag stored inconnection with each of the automatically read ID codes; and sorting theIC devices in accordance with whether their enhanced reliability testingflag indicates they come from an unreliable semiconductor wafer.